Freshwater and marine plants represent important potential sources of food and chemicals. For example in the Orient, macroalgae are consumed extensively as a human food source while in many areas of the world they are used for animal feeds, medicine, animal feed supplements and fertilizers. In the United States, macroalgae are presently used for the production of agar, algin, and carrageenin. Current demand for these useful marine and freshwater macrophytes greatly exceeds their availability, at least on an economical basis. A basic objective of the invention, therefore, is to provide procedures and means for the large scale commercial culture, on an economically feasible basis, of fresh and salt water macrophytes.
Marine and freshwater macrophytes with which the invention may be employed include macro forms in the Subkingdom I Prokaryonta Division Cyanochloronta, Subkingdom II. Chloronta, Division Chlorophycophyta (green algae), Phaeophycophyta (brown algae), Chrysophycophyta Xanthophyceae (yellow green algae), Rhodophycophyta (red algae), Charophyta (stoneworts). Hydrophytic members of Hepatophyta (liverworts), Bryophyta (mosses), Pterophyta (ferns) and Anthophyta (flowering plants) are also included in this invention.
There is one fundamental underlying difference in cultivation technique among hydrophytic members of the various plant classification groups presented above. A number of plants derive nutrition from the water i.e. Chondrus crispus (Rhodophycophyta), Riccia natans (Hepatophyta), Azolla (Pterophyta) and Lemna (Anthophyta). Other plants derive mineral nutrition from the bottom sediments via anchored rhizomes or roots i.e. Watercress (Anthophyta). Intergradations between the two physiological extremes are also known. This invention may be employed for hydrophytes which derive their nutrition from the water or bottom sediments or some intergradation in between.
Chondrus crispus and Gigartina stellata are a source of carrageenin for commercial applications and are of particular interest in this invention. If not found floating in their natural habitat they are found attached to a substrate not by a root system but by a holdfast. Nutrients are not obtained from the bottom sediments but from the surrounding water. Often due to water movement caused by tidal currents, wave action and other forces, these plants are in constant motion which provides maximal exposure to sunlight as well as water bearing nutrients.
We have found that both Chondrus crispus and Gigartina stellata grow faster in water charged atmosphere than underwater under equivalent conditions and grow without attachment as well as obtain nutrients from the surrounding spray or mist.
In accordance with the present invention, freshwater and marine macrophytes are grown in a controlled, substantially closed atmosphere, in which the plants may be continually wetted by a mist or spray or the nutrient-containing water, either fresh or marine, as the case may be. This technique enables optimal conditions of light, temperature and nutrition utilization to be maintained, resulting in greatly enhanced growth rates and harvest cycles as compared to conventional underwater techniques for culturing and harvesting. When freshwater or marine hydrophytes are removed from their native aqueous habitat and furnished a quantity of water-borne nutrients by means of a spray or mist it results in the formation of a thin film of liquid on the plant foliage. The thin film culture technique results in a significant improvement of nutrient utilization and growth rates are greatly enhanced. By comparison, prior efforts to stimulate the growth of macroalgae in their natural environment have proven to be of limited effectiveness, for several reasons: among them, efficient use of nutrient additives is almost impossible to achieve in open water because of the necessity of dispersing sufficient quantities of costly fertilizer into a rather large volume of water, which typically may be subject to at least some degree of current flow which carries the nutrients away from the intended targets. In addition, significant amounts of the fertilizer may be taken up by weed species as well as the cultivated plants, often with undesirable results.
Pursuant to one of the more specific aspects of the invention, nutrient additions may be controllably imparted to the sprayed freshwater or seawater vehicle, not only to enhance growth rates but also to control the desirable product ratio of the plants. In addition to achieving greater nutrient efficiency, one may controllably impart to the sprayed freshwater or seawater vehicle plant growth substances, hormones, antibiotics, fungicides and herbicides. After harvest, shelter sterilizing agents may be introduced prior to restocking the cultivar.
The sun is man's primary source of energy and the amount of energy which reaches the earth's surface is colossal. Unfortunately, when light penetrates water it is subject to the exceptional light absorbing qualities of the water. Even in transparent water free of wave action significant amounts of sunlight are absorbed in the upper layers of water, making limited light available for photosynthesis, particularly when solar energy is relatively low due to variational solar radiation with the seasons and variable cloud cover. Thus, the average efficiency with which plants convert solar energy is low and as a result plants store something like 0.1 to 0.2% of available radiation annually. Plants like the water hyacinth on the other hand may have a very high conversion efficiency given sufficient radiation. In the process of the present invention, cultivation of marine and freshwater hydrophytes in the atmosphere, supplemented by a fine mist or spray, enable greater efficiencies to be realized in the trapping of solar energy, since less solar radiation absorption occurs. Thus, plants grown in the atmosphere in a spray or mist environment will receive more solar energy on a daily as well as seasonal basis.
In general, the apparatus of the invention includes a transparent solar shelter, forming a substantially enclosed atmospheric environment having large roof areas exposed on an axis suitable for achieving maximal solar radiation. Provisions may be made for minimizing the effectiveness of the sunlight during times of intense light, and for enhancing the sun's rays at low angles. Pursuant to the invention, provisions are made inside the transparent solar shelter for maintaining a rather constant fog or mist of freshwater or seawater, supplemented by periodic additions of nutrients and growth substances. For the group of hydrophytes which require rooting in the sediments, the plants are cultivated on the floor of the shelter in either a sediment or hydroponic culture. For the group of plants which obtain nutrition from the water, appropriate racks are provided for holding those plants during the growth cycle and, if desired, the racks may be in the nature of rotatable cylinders or the like.
The use of a spray medium for mariculture has four significant advantages over present aquacultural practices employing water in pools or underwater farming techniques. The most practical advantage is that less water is required (e.g., a cubic foot of seawater, weighs approximately 1000 oz. while a cubic foot of air at 100% relative humidity, 55.degree. F. and one atmospheric pressure contains 0.01 oz. of water vapor). Therefore under theoretical conditions five orders of magnitude less water is required resulting in a significant reduction in cost of heating and cooling. A process employing a water charged atmosphere also allows for more uniform distribution of nutrients to the plants because the control of nutrients in the much smaller quantity of water, is far greater and significant economic benefits are thus realized. Further, since the volume of water employed is minimal in comparison to existing methods, it is economically feasible to utilize filtration techniques, e.g., ultraviolet sterilization and filtration for bacteria, fungi, phytoplankton and zooplankton, control of pathogens or symbionts, etc.
A further advantage of the use of a spray medium is that the particle size of the spray can vary from micron size to raindrop size, and spray nozzles are readily available for this broad range. The new method can make use of several particle sizes, depending on the desired effect. For example, a fine mist can be used for more effective nutrient distribution, and large droplets can be used to "wash" the plants for disease control or when they accumulate particulate matter or extracellular metabolites or organisms lightly attached or clinging to the cultivar. Moreover, if water mist is introduced at temperature A into an air atmosphere at temperature B then the heating/cooling efficiency is a function of heat transfer surface area. Therefore, the fine mist particle size is more efficient than the large particle size in heating and cooling the water charged atmosphere for equivalent masses of water.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments and to the accompanying drawings.